One.relative_identifier(
  1 | 2,
  key: 3 | 4
) | Two.relative_identifier(
  2 | 1,
  key: 4 | 3
)
One.relative_identifier(
  1 | 2,
  key: 3 | 4
)(
  4 | 5,
  key: 6 | 7
) | Two.relative_identifier(
  2 | 1,
  key: 4 | 3
)(
  5 | 4,
  key: 7 | 6
)
One.relative_identifier key: 1 | 2
One.relative_identifier unqualified 1 | 2,
                                    key: 3 | 4
One.relative_identifier 1 | 2,
                        key: 3 | 4